The water begins to increase in the winter, and in the spring it is at the _maximum_. The Trona is best about the commencement of winter, but disappears entirely in the spring. “The lake has diminished in size within the last few years, and if care be not taken, the diminution will soon be much greater. Plants are making considerable encroachments, and very shallow banks are observable in many places. On inquiry, we found the quantity of Trona had not sensibly diminished during the last ten years; but, perhaps, this may be owing to there being always easily found a sufficient quantity of it to supply every demand. The quantity annually exported amounts to between 400 or 500 camel-loads, each being 4 cwt.—a large quantity when the size of the lake is considered. It is removed only when there is a demand. Then a man wades into the lake, breaks off the Trona in large sheets, which he easily does, and hands it to others outside, who are ready to remove all foreign matters, and to pack it in the retecious substance found on the leaves of the date tree. The water of the valley is good, and if a well be dug in the very border of the lake the water is also good, and nearly free from saline impregnation. There are a great many springs in Wady Shiati, and a number in the wadies about Ghaat. All of them, however, were so exposed, that it was impossible to make any correct observations. The maximum heat of Mourzuk is 105 Fah.—a great difference from that mentioned by Captain Lyon. The greatest diurnal change is about 15 degrees—a variation which is pretty regular. The hygrometer of Kater varies from 360 to 410—an amazing small range. My worthy friend Clapperton, sends his kind respects to you, and promises to write you from Bornou. We enjoy the best health, and accomplished our summer’s excursion without fatigue. Remember me kindly to Mr. P. Niell, and tell him the Flora of Fezzan, and of the Tuarick country is very poor; but that in a few months I expect to be on a soil more congenial to the votaries of the fascinating goddess.” TO HIS SISTER. “_Mourzuk, November 4_, 1822.